I'm about to begin DM-ing a new campaign, and one of my players is going to have a changeling PC. As part of the story, the PCs were already going to deal with a hag along the way, and I'm very much a believer in trying to connect the PC's personal stories into the larger campaign. So, I'm thinking about making the hag this PC's mother and having the PC go through the final stages of the Call during the confrontation with the hag. The description in the Changeling information is fairly vague, and I don't want to inflict any crippling penalties on the PC during what is going to be a fairly difficult fight. Any ideas, either rules or RP suggestions, for how to make this a cool encounter and connected to the PC?

I would make it entirely roleplay based. No saves, no checks, no penalties. Just have the hag's message reach her, or say that something is calling out to her but don't explain what. Do your best to make it alluring, desirable, and pleasant. Come up with convincing prospects and explanations so that the call is persuasive.

Any idea on the character herself? Class, alignment? Desires, backstory, hopes, goals, other family?

The PC is going to go Master Spy (taking bard and rogue levels to qualify). Basically, she started hearing the Call some time ago, but having a voice in her head freaked her out, inspiring her to flee home and start living with multiple identities and personas. She's CN and makes her living as an actress (her most open and famous persona) though she also works as a thief and spy. She's joining the party because of personal commitments and a debt she owes to an important NPC. That's all I've got from the player so far!

Okay, so this has been going on for some time, it's not something new the Hag will be starting up just as the party comes into conflict with her. So the PC has become somewhat familiar with the voice in her head (even if she can't stand it and it freaks her out, it's not something new) and is probably aware of what it portends.

The Hag would probably start with making her promises and offers. "You'll have so much more talent and power." "I can give you everything you ever wanted - fame, wealth, knowledge, power, love...." "Aren't you tired of living behind a mask, always having to hide? Aren't you tired of being afraid?" "They only love you now because you're young and beautiful. What are you going to do when you grow old, and they forget all about you?" Things like that.

Find her fears, her desires, her weaknesses, and her dreams, and poke and prod at them, trying to convince her that all she needs for gratification and everything she's ever wanted or needed is to come to Mother and give up her humanity. Try to stay away from threats - don't say stuff like "I'm going to do terrible things to your friends/family/whatever if you don't come", that tends to just make characters push away harder, especially the chaotic ones ;)

Tossing another lead up direction in the pot here - I have a changeling character in my Carrion Crown game that also had to deal with the Call. She never actually reached her mother, but what I would do for her was give her dreams, ones that dealt with the sweet comforting voice. And within these dreams they would gradually become more detailed in that she found herself arriving to her mother, dreamed the transformations but all the while had the feeling that it was natural - that it was meant to be. This of course freaked her out in the waking world. And each time she had these dreams, she sleep walked in the direction of the voice. Therefore someone typically stopped her from actually getting to the location.

As to the encounter itself, that would be an interesting bit. Perhaps if there is spells that the hag has, the changeling may have minuses toward her saves.

Thanks for the ideas and suggestions! I'd thought about doing dream sendings and such as the party moves toward the actual encounter, but I'm not sure how frequently or regularly I would want to do that.

It's definitely a delicate balance of how often to do them. Too often and it looses its specialness and too little loses its potency. I played by ear, but it was easier for me as I was the DM and the changeling was my character.